Degasification of metal



p 6 A. SICKBERT 3,1465% DEGASIF'ICA'I'ION OF METAL Filed Sept. 2'7,196], 4 Sheets-Sheet 1 Jnvenfor:

A0 1. F 5101 Beer Sept L 964 A s ICKBERT DEGASIFICATION OF METAL 4Sheets-Sheet 2 Filed Sept. 27, 1961 p s 1954 A. SICKBERT 3,146,503

DEGASIFICATION OF METAL Filed Sept. 27; 1961 4 Sheets-Sheet 5 Jn vanfor:

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N7 Q r A w MW United States Patent 3,146,593 DEGASIFICATIUN OF METALAdolf Siekbert, Wattenscheid-Eppendorf, Germany, as-

signor to llochumer Verein fuer Gusstahlfabrikation Aktiengesellsciraft,Bochurn, Germany, a corporation of Germany Fiied Sept. 27, 1961, Ser.No. 152,372 Claims priority, application Germany Jan. 24, 1961 6 Claims.(Cl. 22-85) The present invention relates to the degasification ofmetal, for example steel.

Methods have been previously proposed for degassing metal such as steelin Which the molten metal is passed to a degassing device in a transportladle, said degassing device consisting of a vacuum chamber and acharging ladle which is fitted vacuum-tight onto the chamber.

In one known method of this kind steel is electrically heated in thecharging ladle and then flows through the outlet of this ladle into acasting ladle inside a vacuum chamber (see U.S. patent specification2,253,421). If it is not desirable to heat the charging ladleelectrically the loss of temperature incurred during the period ofdegassing has to be made up for by a considerable super-heating of themelt in the furnace. When applying different degassing processes wherereduced pressure is used it is also necessary to account for the loss oftemperature by additional heating. The longer the melt stays in thesecontainers before it is finally cast in moulds the higher the loss oftemperature will be. These necessary and unavoidable excess temperaturesrequire an additional furnace time (heating time), they cause anincreased wear of the refractory lining and prolong the duration of theprocess prior to the casting operation.

The present invention is based on the fact that the otherwise necessaryhigh superheating of the melt can be avoided to a large extent. It ismoreover based on the realisation that the lower the content ofdeoxidizing agent in the steel the quicker and more complete thedegassing process will be. Furthermore a process has already beenproposed whereby a jet of unkilled steel which is subdivided into littledrops is introduced into a vacuum. It was found that it is possible,when carrying out this process in a certain Way, to obtain steel theproperties of which are such that it can be cast into satisfactorycastings at that stage already without any further treatment.

According to one form of the present invention there is provided aprocess for degassing metal under vacuum which comprises melting themetal without applying a vacuum, conveying the molten metal from atapping device to a relatively small feeding device mounted vacuum tighton a vacuum chamber and allowing the molten metal to pass from thefeeding device into the vacuum chamber wherein the molten metal issubjected to a stream degassing operation. The process is applied withadvantage to steel. The relatively small feed device may be funnelshaped.

According to another form of the present invention there is provided anapparatus for carrying out the process, which comprises a tapping devicecooperating with a relatively small feeding device mounted vacuum tighton a vacuum chamber, the vacuum chamber being evacuable by evacuatingmeans. The vacuum chamber may be so designed as to serve both as vacuumchamber and as tapping ladle.

According to a further form of this invention there is provided atapping ladle comprising a stopper device, guiding means for controllingthe movement of the stopper, and a vacuum-tight cover, the tapping ladlebeing designed to serve both as tapping ladle and as a vacuum chamber.

3,146,503 Patented Sept. 1, 1964 The size of the said relatively smallfeeding device is kept as small as possible so that it cannot absorbmuch heat. Furthermore only its lower part need be constantly filledwith molten metal. When tapping the metal which may be melted in anelectric furnace, the outflow rate of the melt is adjusted to correspondto the volume of the said feeding device and its discharge opening.Preferably the molten metal passes through the feeding device quickly.If the pump capacity is sufficient the discharge opening of the feeedingdevice can be left open, as the pump will quickly enough create thenecessary vacuum after the discharge opening has been sealed off by themolten metal. But if desired the discharge opening can be provided witha temporary sealing device, for example a meltable membrane, a valve,for instance a slide valve and/or a stopper rod.

The feeding device is fitted vacuum-tight on the top of the vacuumchamber. This top of the vacuum chamber should have an opening under thedischarge opening of the feeding device.

The vacuum chamber may be so designed as to serve both as vacuum chamberand as a tapping ladle. Thus a suitable ladle having a vacuum-tightcover may be constructed so that a vacuum can be created within theladle. However, if desired, the vacuum chamber may contain a tappingladle.

If the tapping ladle is fitted with a stopper device, sealing means maybe provided underneath the stopper device. When using such a ladle it isadvisable to provide an anti-splash device between the bottom of therelatively small feeding device and the vacuum chamber, the anti-splashdevice passing through the top of the vacuum chamber. The anti-splashdevice serves to protect the ladle stopper device from damage by theinflowing molten metal.

It is also advisable in one embodiment of this invention to cover theladle contained in a vacuum chamber with a heat insulation slab which isprovided with an opening for the inflowing molten metal and which slabshould remain on the ladle until a subsequent casting operation isfinished.

In another embodiment of this invention, instead of using the cover forsealing the tapping ladle directly it can however, also be used forsealing the vacuum chamber into which the ladle is placed.

In one preferred embodiment, the apparatus to be used consistsessentially of a tapping ladle, fitted with a nozzle or a stopperdevice, which ladle is constructed as a vacuum-tight chamber and isprovided with a vacuumtight closing cover. It is expedient to providethe cover with a connecting tube to connect with a vacuum suction pipe.Furthermore a relatively small feeding device which is preferablyconstructed as a feed hopper is arranged on the cover of the vacuumchamber. Preferably this relatively small feeding device is detachableand may be fitted onto the cover with the necessary sealing devices.

In another preferred embodiment, the apparatus consists essentially of avacuum chamber for receiving the tapping ladle and which is fitted witha vacuum-tight cover. Furthermore it consists of a preferablydetachable, relatively small feeding device and as tapping device, achute cooperating with the feeding device with the tapping furnace, oras tapping device a transport device for transporting the molten metalfrom a tapping furnace to the feeding device during the tappingoperation.

Preferably the vacuum chamber is adapted to be transportable and forthis purpose is preferably provided with for example supporting journalsfor engagement with the casting crane, or is so constructed to bereadily movable. It is expedient here for example to have flexibleconnecting tubes and/ or flexible suction pipes which con- I? sistpreferably of swivel joint or ball-and-socket joint like links.

If necessary, especially when treating unkilled steel, the pipesconnecting the vacuum chamber with the pumping unit are cooledappropriately during the tapping operation, preferably by means ofcompressed air pipes which run along the suction pipe and the outletorifices of which are directed towards the suction pipe.

The present invention also provides for the possibility of using onepumping unit for two vacuum treatments if treatment during the tappingoperation as well as during the subsequent casting operation in moulds,e.g. ingot moulds, ceramic moulds or continuous casting moulds, is to beeffected under vacuum. "For this purpose a further suction tube canbranch off the pumping unit or off the pipe leading to the degassingdevice. One or more of such pipes as well as one or more connectingmembers may be provided with shut-oif means, so that such a pipe orconnecting member can be switched to the particular device where thevacuum is needed.

When the tapping operation is completed the metal, e.g. steel, can becast into moulds for instance ingot moulds or continuous casting mouldswhich are in the presence of air, a protective gas or under vacuum.Furthermore a deoxidizing or alloying agent may be added to the moltenmetal before, during or after the degassing operation. When treatingsteel this can be tapped either unkilled, partly deoxidized, orcompletely deoxidized. This can apply to other metals also.-

If steel is tapped in its unkilled state the degassing will beparticularly eifective. Until now it was rather dangerous to transportcompletely unkilled steel in the tapping ladle because the steel wouldvery easily boil up in the ladle. According to the present process,however, even completely unkilled steel can generally be transportedwithout any appreciable danger.

In a preferred embodiment of the process, the steel which is to bedegassed by vacuum treatment is melted in known manner, for example inan electric or openhearth furnace, or in a converter. The steel may flowfrom the furnace in a deoxidized, partly deoxidized or unkilled state;the deoxidizing agent or agents can be added through a feeding device(vacuum-tight sluice). If desired, one or more alloys such as titanium,niobium, boron, aluminium, can also be introduced. If the steel istapped in its unkilled state the degassing operation will beparticularly effective, because a greater part of the deoxidizingprocess takes place over the deoxidizing gaseous phase C of the carbonwhen the molten metal is introduced into the vacuum chamber. It is knownthat this reaction is supported if the inflowing jet is subdivided intosmall drops which provide a large reaction surface. The deoxidizingand/or alloying agent(s) can be added before or during or after thevacuum treatment. Deoxidizing and/or alloying agents can also be addedto the molten metal when casting it into moulds or ingot mouldsafterwards.

In another embodiment of this invention, a chute is used to connect thetap hole of the melting furnace with the upper edge of the relativelysmall feeding device. This chute may be provided with a suspensiondevice so that it can be lowered according to the degree the chute islowered. The part of the chute that is nearest to the feeding device mayrest on an anti-frictional guiding device which may be mounted on ornear the feeding device.

If it is not desirable to use a tapping chute the vacuum chamber may bemounted on a crane or fitted with wheels in order to adjust and controlthe distance between the furnace tap hole and the relatively smallfeeding device during the tapping operation.

In the case of a vacuum tapping ladle which is designed to have astopper device, e.g. stopper rod, it is of particular importance thatthe bearing for the stopper device, e.g. stopper rod, is madevacuum-tight.

In a preferred embodiment of this invention a vacuumtight casing isprovided for the guide rod for the stopper rod along the outside wall ofthe ladle. At the top this casing is connected vacuum-tight in a bore ina flange, which flange is needed with such ladles for the sealingagainst the cover of the ladle. The lower end of the casing is providedwith a vacuum sealing device which encloses the guide rod, which in turnhas a circular crosssection. Preferably the sealing device is designedas a packing box. It is expedient to use a particularly soft packinggland. During the vacuum treatment in the tapping ladle the sealingdevice is tightly screwed onto the soft gland by means of a cap nut, andhas to be loosened before starting the casting operation to permit aneasier movement of the rod.

In a further embodiment of this invention the suction pipe between thevacuum pumping unit and the vacuum chamber of vacuum tapping ladle maybe cooled. In certain cases this cooling may be limited to the vicinityof the tapping ladle. Cooling is particularly expedient when treatingsteel, and especially when treating unkilled steel.

According to one embodiment of this invention the cooling effect isachieved by means of pipes which blow air onto the suction pipe, the airbeing supplied by nozzles. In the case of flexible lines these pipes areappropriately fitted along the lines. In the case of lines with swiveljoint or ball-and-socket joint-like parts the pipes for the coolingagent can be correspondingly flexible and follow the bends of theflexible suction tube.

According to another embodiment of this invention the same pumping unitcan be used for the first vacuum treatment after the tapping as well asfor a subsequent or all subsequent degassing operations. The need forsuch subsequent degassing operations which are preferably carried out atlower rates of pressure arises particularly in the case of casting fromthe vacuum tapping ladle. As the larger portion of the gas has beenremoved during the vacuum treatment after the tapping opera tion it ispossible and very advantageous to apply a particularly low pressure whenvacuum casting from the tapping vacuum ladle, so that the pressure iswell below that used previously in the vacuum tapping ladle.

The present invention can be carried out in several dilferent ways.

If only one line (flexible) is used this line can be provided with aconnecting member which can be connected with both the vacuum tappingladle and the vacuum feeding device.

However it is also possible to provide a second suction pipe to thevacuum feeding device which branches off from the pumping unit or fromthe suction pipe of the pumping unit which leads to the vacuum tappingladle.

In the latter case, a possibility has to be provided for switching thesuction pipes on and off individually, which can for example be achievedby means of a vacuum-tight shut-01f valve which is fitted in each of thesuction pipes. This advantageous mode of operation constitutes anessential simplification of the dual degassing processthe first of whichis carried out after the tapping and the: second during the subsequentcasting process from thetapping ladle into moulds, ingot moulds orcontinuous. casting moulds, under vacuum.

With respect to the above mentioned possibility of be determined byadjusting the pressure accordingly. The casting into slabs, billets orbars is effected in a known way in the presence of air or protective gasand preferably with the aid of a tun-dish. In most cases the pressurewill be adjusted so as to allow for a considerably large unsegregatedzone to remain inside the slab, billet or bar. If desired the processcan be controlled so that the casting solidifies practicallyunsegregated across its whole cross-section.

This method described immediately above offers the particular advantageof heat economy. Despite an additional operationthe evacuationnosubstantial loss of heat is incurred as compared with the conventionalcontinuous casting methods. Furthermore this treatment makes it possibleto adjust diiferences in quality between the individual melts whichusually occur in continuous production and to improve the overallquality which results in a uniform quality of the slab, billet or barand of the finished products made therefrom, e.g. strip or wire.

The accompanying drawings show various embodiments of the thisinvention.

FIG. 1 shows in diagrammatic sectional elevation an apparatus comprisinga tapping vacuum ladle, i.e. a device in which a vacuum is created onlywithin the ladle;

FIG. 2 shows diagrammatically in side elevation a flexible line betweenthe vacuum chamber and the pumping unit (not shown);

FIG. 3 shows diagrammatically in plan view a ing device for the flexibleline according to FIG. 2;

FIG. 4 shows in diagrammatic sectional elevation an apparatus comprisinga vacuum-tight stopper guiding means for a vacuum tapping operationaccording to FIG. 1;

FIG. 5 shows in diagrammatic sectional elevation an apparatus comprisinga tapping ladle inserted and enclosed by a vacuum chamber; and

FIG. 6 shows in diagrammatic sectional elevation a modification of theapparatus illustrated by FIG. 5.

Referring to FIG. 1, a tapping ladle 1 which is designed as avacuum-tight chamber has a vacuum-tight cover 2 which is provided with aconnecting tubular elbow 3 to connect the cover 2 with suction pipe 4.Connecting elbow 3 is also provided with a valve 6. Connecting elbow 3and/ or suction pipe 4 is/ are made of a flexible material and is/ arepreferably fitted with swivel joint or ball-and-socket joint like links15 (according to FIG. 2). Arranged on cover 2 is a relatively smallfunnel-shaped feeding device 5, the stopper rod 13 of which is optional.Under the discharge opening of the feeding device 5 a sealing device 9is fitted which can be removed when the melt is introduced. Underneaththe outlet of the feeding device 5 an antisplash device 7 is providedwhich protects the stopper device 8 from damage. A sealing device 10 isfitted under stopper device 8. Furthermore a feeding means 11 isprovided for the addition of an alloying or deoxidizing agent and a TVcamera 12 to permit control of the degassing operation. The feedingdevice 5 is connected to an overflow chute 14, especially for slag.

The flexible connection according to FIG. 2 is not shown in FIG. 1. Itis needed for example during the tapping operation when it allows theapparatus to follow the movements of a tapping chute 16. According toFIG. 2 the flexible pipe consists of tubular members 4 which areconnected by links 15, in this case swivel joints.

After the completion of the tapping operation the cover 2 can beremoved, and the casting operation can be effected in the usual way. Itis however, also possible to disconnect the connection with the pumpingunit, then remove the whole apparatus and proceed with the castingoperation with the cover still on.

Whereas FIG. 2 is a side view of the flexible pipe, FIG. 3 shows thesame pipe in a plan view. According to FIG. 3 pipes 17 are disposedalong tubular memcoold bers 4 of the flexible suction line, and acooling agent 18 can be blown onto the tubular members 4 of the suctionline through openings 19. The cooling pipes 17 are also provided withlinks 20 so that they can follow the movement of tubular members 4 andlinks 15.

FIG. 4 shows an embodiment of a vacuum-tight guiding means for thestopper rod of a tapping vacuum ladle 1. This ladle is provided with acover 2 which rests in a sealing member 23 in a flange 24. This flange24 has a bore 25 into which the casing 26 of the stopper rod guiding rod27 is fitted in a vacuum-tight manner. The cross-section of the portionof rod 27 near flange 24 is angular, but it changes and becomes circularnear point 28. At the lower end of casing 26 a packing box 29 isconnected vacuum-tight with the casing 26 by means of a soft packing 30and a cap nut 31. The guiding rod 27 is fitted with another guidingmeans 32. As usual the guide rod 27 is connected with a crosshead 33which in turn is connected with stopper rod 8.

FIG. 5 shows an apparatus in which a tapping ladle 46 is inserted into avacuum chamber 41 which is provided with a cover 2.

In this case the cover 2 is hinged to the vacuum chamber 41 by means ofjoint 60 so that it can be moved back when the chamber 41 is opened.Furthermore a feed opening 45 is provided in the cover 2 with anantisplash device 7. A relatively small feeding device 47 is fastenedonto the cover 2 in a vacuum-tight manner at 48. The feeding device 47is also provided with a bracket 49 which has a guiding means 50 for aconnecting chute 51. This connecting chute is connected to tapping spout52 by means of links 53 so that it can be lowered to the position shownin chain dotted lines in accordance with the lowering of the tappingspout. The connecting tube for the suction pipe is denoted 3.

FIG. 6 represents a vacuum chamber 41 which consists of a base plate 56,a centrepiece 57 and a cover 2. In this case a feeding device 47 issealed neither by a stopper above the outlet 54 nor by a sealing devicebeneath the outlet 54. Consequently the first charge of molten steelthat enters the feeding device 47 has to seal off the outlet 54 before avery efficient pumping unit starts operating and evacuates the container41.

It is also possible to design a vacuum chamber, the centrepiece 57 andthe cover 2 of which constitute one unit, so that a sealing device isonly needed at the base plate 56.

It may be mentioned here that especially when degassing unkilled steelthe anti-splash device referred to in the particular description andillustrated in the drawings may be formed as a double-walled tube incase of damage by the molten steel to the inner wall.

It is possible to combine the degasification with a desulphurizingtreatment. Known desulphurizing means, such as a mixture of lime andfluorspar, may be added into the tapping ladle before and/or duringtapping. F.i., a steel having a sulphur content of 0.015% was treatedwith a mixture of 4 parts lime and 1 part fluorspar in a quantity of 2%of the steel weight. The final sulphur content was 0.003%.

What I claim and desire to secure by Letters Patent is:

1. In a tapping ladle provided with a discharge opening through itsbottom and having an axially movable stopper rod for control of thedischarge opening, in combination therewith, the improvement whichcomprises a sealing flange surrounding said ladle, a cover removablypositioned in vacuum-tight engagement with said sealing flange, a tubeextending alongside said ladle through said flange, an axially movablecontrol rod extending through said tube into said cover, a cross memberconnecting said control rod and said stopper rod and a sealing memberforming a vacuum-tight sliding seal between said control rod and tube.

2. Improvement according to claim 1 in which said tube and control rodhave corresponding non-circular adjacent cross-sectional areas to allowa sliding nonrotating fit therebetween.

3. Improvement according to claim 2 in which the portion of said tubeextending through said flange has .a non-circular cross-sectional shapeand the adjacent portion of said control rod has a correspondinglyshaped cross-sectional shape.

4. Improvement according to claim 3 in which said sealing member is apacking gland positioned at the lower end of said tube.

5. Improvement according to claim 1, in which said sealing member is apacking gland positioned at the lower end of said tube.

6. Improvement according to claim 1, said sealing member including apacking box fixedly secured with respect to the tube, packing materialwithin the packing box, and a cap nut adjustable between a firstposition in which the packing material tightly grips the control rodassuring a vacuum-tight seal and a second position permitting movementof the control rod to actuate the stopper rod.

References Cited in the file of this patent UNITED STATES PATENTS2,253,421 De Mare Aug. 19, 1941 2,290,961 Heuer July 28, 1942 2,322,618De Mare June 22, 1943 2,832,110 Carleton Apr. 29, 1958 2,837,790 RozianJune 10, 1958 2,962,779 Hornak et a1. Dec. 6, 1960 2,966,709 Ruppel etal. Jan. 6, 1961 FOREIGN PATENTS 74,274 France Nov. 7, 1960 469,762Canada Nov. 28, 1950 609,687 Canada Nov. 29, 1960 1,236,229 France June7, 1960 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N03' 146,503 I September I 1964 Adolf Sickbert It is hereby certified thaterror appears in the above numbered patent requiring correction and thatthe said Letters Patent should read as corrected below.

Column 4, line 18 for "of vacuum read or vacuum Signed and sealed this9th day of February 1965u (SEAL) Attest:

ERNEST W. SWIDER' EDWARD J. BRENNER Attesting Officer Commissioner ofPatents

1. IN A TAPPING LADLE PROVIDED WITH A DISCHARGE OPENING THROUGH ITSBOTTOM AND HAVING AN AXIALLY MOVABLE STOPPER ROD FOR CONTROL OF THEDISCHARGE OPENING, IN COMBINATION THEREWITH, THE IMPROVEMENT WHICHCOMPRISES A SEALING FLANGE SURROUNDING SAID LADLE, A COVER REMOVABLYPOSITIONED IN VACUUM-TIGHT ENGAGEMENT WITH SAID SEALING FLANGE, A TUBEEXTENDING ALONGSIDE SAID LADLE THROUGH SAID FLANGE, AN AXIALLY MOVABLECONTROL ROD EXTENDING THROUGH SAID TUBE INTO SAID COVER, A CROSS MEMBERCONNECTING SAID CONTROL ROD AND SAUD STOPPER ROD AND A SEALING MEMBERFORMING A VACUUM-TIGHT SLIDING SEAL BETWEEN SAID CONTROL ROD AND TUBE.